The invention relates to a weather strip for an automobile, comprising a slightly foamed solid rubber portion with a core bar embedded therein, and a continuous extrusion molding system for molding the same.
On the basis of FIGS. 1 to 3, the related art is described hereinafter referring to FIG. 5. When a weather strip 20 for an automobile, comprising a U-shaped trim 2 formed by embedding a core bar 4 in a slightly foamed solid rubber portion 3, is molded with a continuous extrusion molding system, a void 21 is prone to occur to a boundary part between the core bar 4 and the slightly foamed solid rubber portion 3 due to a gas pocket formed. The reason for this is because a blowing agent contained in the slightly foamed solid rubber portion 3 is gasified as a result of being heated up by heat generated at the time of extrusion molding with an extruder 11, and being heated up in a vulcanizing furnace 15, and gas thus generated in part of the slightly foamed solid rubber portion 3, in close proximity to the core bar 4, is not turned into bubbles, thereby gathering towards the core bar 4.
The void 21 tends to occur in a groove bottom 3a of a U-like shape of a part of the slightly foamed solid rubber portion 3, substantially resembling the letter U, taking a tunnel form at times, or occurring at a number of successive places to a size in the order of 5 mm at other times. In case that the void 21 occurs to the slightly foamed solid rubber portion 3, the slightly foamed solid rubber portion 3 is peeled off from the core bar 4, and will be in floating condition, causing difficulty with conveying holding force of rubber to the core bar 4 when pushing out the core bar 4 at the time of extrusion molding, that is, at the time of breakout, so that the breakout of the core bar 4 can not be implemented with ease. If the holding force is increased for that reason, the surface of the slightly foamed solid rubber portion 3 is prone to be marred with holding marks, thereby aggravating external appearance. In addition, presence of the void 21 interferes with attachment of the weather strip to a flange. Further, if the void 21 occurs to an outer part 3b of the solid rubber portion 3, this also will result in poor external appearance.
A thermoplastic elastomer comprises a rubber component (soft segment) for exhibiting elasticity, and a resin component (hard segment) for fluidizing at a high temperature and blocking plastic deformation at room temperature, and the same is material that can be plasticized at high temperature to be molded in the same way as a thermoplastic resin. A thermoplastic elastomer containing olefin-based components is called an olefin thermoplastic elastomer (referred to as TPO).
Thus, with the weather strip 20 for the automobile, comprising the slightly foamed solid rubber portion 3 with the core bar 4 embedded therein, that is extrusion molded with the conventional continuous extrusion molding system, the void 21 is prone to occur to the boundary part between the core bar 4 and the slightly foamed solid rubber portion 3, and interferes with the attachment of the weather strip to the flange, resulting in poor external appearance. It is therefore an object of the invention to provide a weather strip causing no such problems, and a continuous extrusion molding system for molding the same.
Referring to FIGS. 1, 2, 4, and 5, description is given hereinafter. In the first aspect of the invention, there is provided a weather strip 1 for an automobile comprising a U-shaped trim 2 formed by embedding a core bar 4 in a slightly foamed solid rubber portion 3, foamed so as to have a specific gravity of 0.8 to 1.2, wherein tiny holes 7 having a depth reaching the core bar 4 are defined in part of the slightly foamed solid rubber portion 3, within the U-shaped trim 2, in such a way as to be arranged in line along the longitudinal direction of the weather strip 1.
With the weather strip 1 for the automobile, having those features, tiny holes 7 having a depth reaching the core bar 4 are defined in a groove bottom of a U-like shape of part of the slightly foamed solid rubber portion, within the U-shaped trim, in such a way as to be arranged in line along the longitudinal direction of the weather strip 1.
Further, with the weather strip 1 for the automobile, having those features, tiny holes 7 having a depth reaching the core bar 4 may be defined in an outer part 3b of the slightly foamed solid rubber portion 3, visible from outside, in such a way as to be arranged in line along the longitudinal direction of the weather strip 1, and the tiny holes 7 are preferably sealed with a coating 8 formed of a thermoplastic elastomer or resin.
The invention provides in its second aspect a continuous extrusion molding system 10 for continuously extrusion molding a weather strip 1 for an automobile, comprising the U-shaped trim 2 formed by embedding a core bar 4 in a slightly foamed solid rubber portion 3, comprising a prickly gear 13, rotatable while pressed in contact with the weather strip 1 being extruded, and disposed so as to be adjacent to a mouth piece 12 of an extruder 11, wherein tiny holes 7 having a depth reaching the core bar 4 are defined in part of the slightly foamed solid rubber portion 3, within the U-shaped trim 2, in such a way as to be arranged in line along the longitudinal direction of the weather strip 1 by use of the prickly gear 13.
Further, with the continuous extrusion molding system 10 having those features, tiny holes 7 may be sealed with a coating 8 formed of a thermoplastic elastomer or resin, formed on the surface of the slightly foamed solid rubber portion 3, by use of a coating unit 16 after the tiny holes 7 having the depth reaching the core bar 4 are defined in part of the slightly foamed solid rubber portion 3, within the U-shaped trim 2, in such a way as to be arranged in line along the longitudinal direction of the weather strip 1 by use of the prickly gear 13.